iPod Nano 16gb For Spares/Repair (ME9)

I don't believe this iPod Nano has ever been used, but I took it out the packet so that I could check that it still works.
You will see from the picture that there's a slight shadow top left and I believe this is a sign that the battery may be swelling.
If this is the case, I probably shouldn't have tried charging it but I did and after 45 minutes of charging when I unplugged it it turned off so it's not holding a charge at all.
It's such a shame because this item is like new and it's never been used.
I'm wondering if there are any tinkerers out there who are able to get into it and replace the battery and enjoy this lovely piece of retro tech.
I'm giving it away with its original box and the earphones but I'm keeping the charger because that actually is for my iPod Classic which I still use at Christmas haha!